渤海湾盆地古近纪古地理特征与油气*

渤海湾盆地是一个典型的内陆裂谷盆地,内部发育6个坳陷、4个隆起、54个凹陷和44个凸起。沉积盆地的含油气性与其古地理分布有密切的关系。利用渤海湾盆地各坳陷大量的录井、岩心、古生物、测井、地震资料及前人的大量文献和数据,对渤海湾盆地各坳陷古近系孔店组、沙河街组沙四段、沙三段、沙二段、沙一段、东营组进行了全区对比和统层。在此基础上,对冀中坳陷、济阳坳陷、临清坳陷内东濮凹陷各组段的沉积相进行了分析,编制了这些区域的古地理图;充分利用前人文献和科研报告中所编制的辽河坳陷、黄骅坳陷、渤海海域古近系各组段的古地理图,编制了渤海湾盆地孔店组、沙河街组沙四段、沙三段、沙二段、沙一段、东营组的古地理图。渤海湾盆地发育数十个含油气凹陷,每个凹陷中心的深湖亚相泥岩构成烃源岩,而在凹陷的边缘发育近岸水下扇、扇三角洲、三角洲、滩坝等砂体,构成重要的储集层,在有利的成藏条件下,凹陷中央的烃源岩向周围与之互层的储集层供烃形成油藏,在凹陷中央的烃源岩中,还发育了页岩油、页岩气、致密油气等非常规油气。因此,每个凹陷就是油气生成、运聚的基本单元,是一个独立的油气运移—聚集系统。生油凹陷的分布及其古地理特征控制了油气在渤海湾盆地古近系中的平面分布。

Paleogene palaeogeography and oil and gas distribution in Bohai Bay Basin

The Bohai Bay Basin is a typical inner-continent rift basin characterized by six depressions,four uplifts,54 sub-depressions and 44 sub-uplifts. The hydrocarbon distributions are closely related to their palaeogeography. In this paper,integration of a large number of well logging,core,paleontological and seismic data in various depressions in Bohai Bay Basin,as well as a large number of published data,were used to correlate and build the Paleogene(including the Kongdian,Shahejie and Dongying Formations)stratigraphic framework in each depression in Bohai Bay Basin. On this basis,the sedimentary facies of each formation and member of the Paleogene in the Jizhong Depression,Jiyang Depression,and Dongpu sub-depression of Linqing Depression were analyzed,and the sedimentary system map of these areas was compiled. Combined with previously published palaeogeographic reconstruction of the Liaohe Depression,Huanghua Depression and the Bohai Sea area,the lithofacies palaeogeographic map of the Kongdian Formation,the Members 4,3,2,1 of Shahejie Formation,and Dongying Formation of the Paleogene in the Bohai Bay Basin were compiled. There are dozens of oil and gas-bearing sags in the Bohai Bay Basin. The deep lacustrine mudstone in the center of each sag constitutes the source rocks,while the nearshore sublacustrine fans,fan deltas,deltas,beach bars and other sand bodies on the sag margin are important reservoirs. Under favorable accumulation conditions,the source rock in the center of the sag supplies hydrocarbons to the surrounding interbedded reservoirs to form oil reservoirs. In the center of the sag,unconventional hydrocarbon resources such as shale oil,shale gas,and tight oil and gas are also developed. Therefore,each depression is the basic unit of oil and gas generation,migration and accumulation,and an independent oil and gas migration-accumulation system. The distribution of oil-generating sags and their palaeogeographic features control the planar distribution of oil and gas in the Paleogene in the Bohai Bay Basin.